Atomic force microscopy of the bacterial photosynthetic apparatus: plain pictures of an elaborate machinery

Photosynthesis both in the past and present provides the vast majority of the energy used on the planet. The purple photosynthetic bacteria are a group of organisms that are able to perform photosynthesis using a particularly simple system that has been much studied. The main molecular constituents required for photosynthesis in these organisms are a small number of transmembrane pigment-protein complexes. These are able to function together with a high quantum efficiency (about 95%) to convert light energy into chemical potential energy. While the structure of the various proteins have been solved for several years, direct studies of the supramolecular assembly of these complexes in native membranes needed maturity of the atomic force microscope (AFM). Here, we review the novel findings and the direct conclusions that could be drawn from high-resolution AFM analysis of photosynthetic membranes. These conclusions rely on the possibility that the AFM brings of obtaining molecular resolution images of large membrane areas and thereby bridging the resolution gap between atomic structures and cellular ultrastructure.